1. Field of the Invention
The present invention relates generally to a rotary sorption concentrator system and in particular, to a rotary bed sorption system that includes in-situ high temperature regeneration of the rotary concentrator adsorbent media.
2. Description of the Related Art
Rotary sorption concentrator systems have long been used in the art and uses an established technology. Such systems typically collect a sorbate from one fluid stream, sometimes called a process or sorption fluid stream, and transfer it in a more concentrated form to a second fluid stream, sometimes called a desorption fluid stream. Commonly removed sorbates includes volatile organic compounds (“VOCs”).
Rotary concentrator technology offers concentrating abilities and operating efficiencies as compared to other techniques. It is particularly useful in low-concentration exhaust streams, where VOCs with low to medium range boiling points are present. Such exhaust streams occur, for example in semiconductor manufacturing and paint booth exhaust streams. The basic technology offers significant fuel savings, which is driving the industry to broaden the application base for rotor concentrators into treating exhaust streams containing high boiling point or polymerizing VOCs in their exhaust streams.
In a typical rotor concentrator system the adsorbent material or media is housed within a rotor housing which is divided into a plurality of rotor treatment zones and the rotor rotates in a cycle of operation on a continuous basis. The VOC-laden process airstream passes through the process zone where the VOCs are retained on the rotor media and cleaned process air exits the rotor.
After passing through the process zone, the rotor enters the desorption zone through which a desorption airstream passes. The desorption airstream is heated to a sufficient temperature (typically 250 to 400° F.) before entering the media and strips or re-volatilizes the VOCs from the rotor media. The desorption airstream is typically 1/10th of the volume of the process airstream, although smaller percentages are also commonly used. The desorption airstream is heated from a heat exchanger in the exhaust airstream of an oxidizer, which is a separate device in which heat is recovered, or other by methods. Once the desorption airstream exits the media, having entrained the VOCs, it is known as the concentrate airstream. This concentrate airstream is directed to the final treatment device, typically an oxidizer of known construction, which oxidizes the contaminants at a high temperature to form carbon dioxide (CO2) and water which can be exhausted to the atmosphere.
With high boiling point VOCs, polymerizing VOCs (such as styrene) and other entrained contaminants (such as paint overspray) there is a concern that the VOCs may not be fully desorbed from the rotor adsorbent media under the normal operation mode of the system because the temperature of the desorption fluid stream of known systems is not sufficiently high. (Fluid in this context includes air or other gaseous streams.) Therefore, the retained compounds will block the adsorption sites in the adsorption media, reducing the media's adsorption efficiency. Clogging of the rotor media's substrate can also occur. That would increase the pressure drop across the rotor. Such a pressure increase can cause operational imbalances throughout the system and increase power consumption of the air moving devices. Removal of these VOCs and contaminants upstream of the rotor system may not be possible or may be undesirable, as it requires the additional expense, installation and maintenance of extra equipment (such as a condenser.)
In circumstances where VOCs and contaminants are retained in the rotor media despite the conventional desorption process, it is desirable to return the media to its original state, free of VOCs, contaminants, organics, etc. Such regeneration of the rotor media also avoids expensive replacement costs. To date, rotor concentrator media regeneration has typically been achieved through either a washing process or ex-situ heating process.
In order to remove excess contaminants from sorbate rotors, one prior U.S. Pat. No. 7,018,447, describes a method for washing the rotor in-situ while it is on-line. According to that patent, a washing agent is introduced into the desorption section of the rotor that is then rotated 360° plus a sector. Then that sector is washed. The method continues until all sectors have been washed. The wash is a mild detergent or acid. This process results in a liquid waste stream as a by-product of the process. The liquid waste stream needs to be collected from the housing of the equipment and then disposed of as hazardous waste. This requires additional collection equipment and the need for processes and procedures for disposal of the liquid waste.
In the more typical ex-situ heating process for cleaning rotors, the rotor media is physically removed from its housing and transported to another location. At that location, the media is exposed to a high temperature for a period of time required to remove the contaminants. This process requires a considerable labor expense and a significant amount of downtime for the system, while the rotor media is being treated. Permanent damage to the media, requiring replacement, is also possible with the ex-situ heating process if special handling procedures are not maintained or if the internal temperature of the media is not controlled properly.